Carpet and textile fibers are easily soiled and stained in everyday use. The problem of fiber soiling has become more difficult with the advent of synthetic fibers such as polypropylene, polyamide, polyethylene, and polyester, that are substantially more oleophilic (oil-loving) than traditional natural fibers such as cotton and wool.
A wide variety of materials are known to cause soiling. Soil found on fibers can include a variety of solid particles, such as fly ash or other inorganic particulates; liquids, such as oils and greases; mixtures of solids and liquids, such as soot (that contain particles mixed with oily components); and biological matter suchas skin cells and sebum.
Soil typically adheres to the fiber surface by Van der Waals forces, that are effective only over very short distances. The strength of the bond depends on the forces of interaction per unit interfacial area, the area of contact, and whether a liquid is present on the fiber surface. Oily films on the fiber increase soiling. In general, the higher the viscosity of the liquid, the greater the adhesion of the liquid to the fiber. Soil particles can even adhere to initially smooth surfaces, such as polyester and polyethylene film. Soil is not commonly mechanically entrapped in the fiber.
Staining of a fiber can occur in a wide variety of ways, including through the ionic or covalent binding of an exogenous colored substance to the fiber. For example, nylon fibers are polyamides with terminal amino and carboxyl end groups. Nylon is commonly stained by acid dyes, which are colored, negatively charged molecules that ionically bind to the protonated terminal amine. Examples of staining acid dyes include liquids containing FD&C Red Dye No. 4, wine, and mustard.
For many years, soil (as opposed to stain) resistance has been imparted to carpet and textile fibers by applying a finish that repels oil and water. Perhaps the first soil resist agent for fibers was starch, that was removed along with the soil when the fiber was washed. Other water soluble polymeric stain resist finishes have included methylcellulose, hydroxypropyl starch, polyvinyl alcohol, alginic acid, hydroxyethyl cellulose, and sodium carboxymethyl cellulose. As with starch, the strong disadvantage of these protective finishes is that their mechanism of action is sacrificial; they contain the soil but are removed along with it when the fiber is cleaned.
Vinyl polymers including acrylics, methacrylics and polymers of maleic acid have also been used as soil release agents. U.S. Pat. No. 3,377,249 discloses emulsions of copolymers of ethyl acrylate with at least 20% acrylic, methacrylic, or itaconic acid in combination with N-methylol acrylamide.
More recently, fluorochemical soil release agents have become very popular. The fluorochemical agents are coated onto the fiber to prevent wetting of the surface by minimizing chemical contact between the surface and substances that can soil the carpet, making the substance easier to remove.
The first fluorochemical finishes focused on reducing the surface energy of the fiber to prevent the spreading of oily soils. More recently developed fluorochemical finishes have attempted to combine reduction in surface energy with hydrophilicity, as described in U.S. Pat. No. 3,728,151. A number of patents describe fluorinated polymers for use as soil resist coatings for fibers, including U.S. Pat. No. 3,759,874 (describing polyurethanes that consist of a combination of an oleophilic fluorine-containing block and a hydrophilic polyethyleneoxide block) and U.S. Pat. No. 4,046,944 (describing a fluorinated condensation block copolymer, that include oleophilic fluorinated blocks and hydrophilic polyethyleneoxide blocks connected by urea linkages).
Although fluorinated finishing coats on fibers do impart an amount of soil resistance to the fiber, they all suffer from the distinct disadvantage that they are removed by routine maintenance of the fiber. None of the fluorochemical finishes available to date provides permanent protection from soiling and staining. This is a particular problem for polypropylene, that is very oleophilic, and that has begun to compete with nylon as a fiber for use in residential carpets.
Thermoplastic polymer fibers are frequently treated with fluorochemical compounds in order to affect the surface characteristics of the fiber, for example to improve water repellency or to impart stain or dry soil resistance. Most frequently, fluorochemical dispersions are applied topically to the fabrics made from these fibers by spraying, padding or foaming, followed by a drying step to remove water.
For example, a method is known for obtaining dry soil resistance and nonflame propagating characteristics in a textile fiber by applying topically aqueous dispersions of a variety of fluorinated esters derived from perfluoroalkyl aliphatic alcohols of the formula CnF2n+1 (CH2)mOH where n is from about 3 to 14 and m is 1 to 3, together with mono- or polycarboxylic acids which contain from 3 to 30 carbons and can contain other substituents. The fluorinated esters include, among others, a perfluoroalkylethyl stearate corresponding to “ZONYL” FTS available from DuPont, as well as perfluoroalkylethyl diesters made from dodecanedioic acid or tridecanedioic acid.
It is well recognized that the process of manufacturing thermoplastic polymeric fibers and fabrics could be simplified and significant capital investment could be eliminated if the topical application were replaced by incorporating a fluorochemical additive into the polymer melt prior to the extrusion of the fiber. The difficulty has been in finding suitably effective fluorochemical additives.
Thermoplastic polymers include, among others, polyolefins, polyesters, polyamides and polyacrylates. Polyolefins, and in particular polypropylene, are frequently used for disposable nonwoven protective garments, particularly in the medical/surgical field, in part because of a polyolefin's inherent water-repellency. However, polyolefins are not inherently good repellents for other lower surface tension fluids frequently encountered in the medical field such as blood and isopropyl alcohol. To get around this deficiency, fluorochemical dispersions are applied topically to these fabrics.
The requirements of an additive suitable for incorporating into a polyolefin melt include, besides the ability to repel low surface tension fluids at a low concentration of the additive, a satisfactory thermal stability and low volatility to withstand processing conditions. Preferably the compound will migrate to the surface of the fiber so as to minimize the amount of additive needed for adequate repellency. While this migration can often be enhanced by post-extrusion heating of the fiber, it is more preferable for the migration to occur without the need for this heating step. This requirement for mobility in the polymeric fiber in turn tends to limit the size of the fluorochemical molecule, and effectively eliminates from consideration high molecular weight polymeric fluorochemical additives.
The general concept of incorporating fluorochemical additives into a polyolefin fiber melt is known, but the difficulty in finding suitable effective additives has limited the application of this concept. Many of the past efforts to evaluate such fluorochemical additives have been aimed at improving other properties of the polyolefin, and do not teach methods of its improving repellency to low surface tension fluids.
Nonwoven composite structures are known consisting in part of two or more melt-extruded nonwoven layers, at least one of which includes an additive which imparts to the surface at least one characteristic different than the surface characteristics of the polymer alone as a result of preferential migration of the additive to the surface without the need for post-formation treatment of any kind. Examples of the additive-including layer include polypropylene modified by commercially available fluorochemical additives, including “ZONYL” FTS defined above.
U.S. Pat. Nos. 5,178,931 and 5,178,932 disclose specific nonwoven laminiferous and composite structures respectively, consisting in part of three melt-extruded nonwoven layers, the second of which includes an additive which imparts alcohol repellency as a result of preferential migration of the additive to the surface without the need for post-formation treatment of any kind, and where at least one of the first and third layers has been treated by topical application of an agent to change its characteristics in some way. Examples of the additive-including second layer include commercially available fluorochemicals, including “ZONYL” FTS.
Soil resistant polymeric compositions are known which are prepared by melt extrusion with a nonpolymeric fluorochemical dispersed throughout the polymer. The polymers used include polypropylene, polyethylene, polyamide and polyester, and the fluorochemical used is a perfluoroalkylstearate, in particular “ZONYL” FTS.
In addition, a polymeric composition is known comprising a mixture of a polymer selected from the group of polypropylene, polyethylene, polyamide and polyester with a fluorochemical comprising a fluorinated oleophobic, hydrophobic alkyl group attached to a nonfluorinated oleophilic alkyl, aryl, aralkyl or alkaryl moiety optionally through a linking moiety, which can be melt extruded as a mixture. A more specific description of the above fluorochemical is not disclosed, but among the many compounds which are applicable are esters where the oleophilic organic group contains from 2 to 35 carbon atoms. Examples of such are “ZONYL” FTS or a product made by transesterifying “ZONYL” BA with methyl stearate and methyl palmitate.
An automotive coating film is known containing an organic solvent-soluble waxy hydrocarbon which possesses a fluorine-containing organic group. This component is a product obtained by esterifying and coupling a high molecular weight alcohol with a carboxylic acid which possesses a fluorine-containing group or a product obtained by esterifying and coupling a high molecular weight fatty acid and an alcohol which possesses a fluorine-containing group. As examples of high molecular weight alcohols included are those with average carbon chain lengths with up to 50 carbons. As examples of high molecular weight fatty acids included are those with carbon chain lengths of up to 31 carbons (mellisic acid). The products were tested only as a waxing agent for automobiles.
Japanese Patent Application 3-41160 teaches a thermoplastic resin composition containing a perfluoroalkyl group-containing long chain fatty ester of the formula Rf—R1—OCO—R2 where Rf is a perfluoroalkyl group with 5 to 16 carbons, R1 is an alkylene group with 1 to 4 carbons, and R2 is an unsaturated alkyl group or a saturated alkyl group with 21 to 50 carbons. One example reacts C8F17C2H4OH with C27H55COOH to produce the ester. The resins included polyethylene and polypropylene. Benefits of the additive were shown by the contact angle of water with molded articles of the resin. No tests are reported on the repellency to low surface tension fluids of the resulting polymers.
A need exists to achieve superior repellency to low surface tension fluids and superior product efficiency.
In summary, while the prior art discloses numerous examples of polyolefin fibers containing a fluorochemical additive incorporated at the melt stage to alter the surface characteristics of the extruded fiber, much of this was aimed at soiling and staining resistance, water repellency or other purposes.
U.S. Pat. Nos. 5,560,992 and 5,977,390 disclose soil resistant thermoplastic polymers containing a fluorochemical.